Antonio Maria Costa, the Executive Director of the United Nation's Office on Drugs and Crime, said he had "mounting evidence of drug money being used to finance criminal activities, including terrorism".
Costa was speaking on Friday before addressing the International Conference on Counter-Narcotics in Afghanistan, being held in Kabul on Sunday and Monday. He will also hold direct talks with leading Afghan officials.
"If we don't start translating counter-narcotics commitment into lower levels of production, we run the risk of (an) opium economy undermining all that has been achieved in creating a democratic new Afghanistan," he said.
But Costa hailed several government measures, including Afghanistan's new anti-drug laws and the adoption of the National Drug Control Strategy, which aims to completely eliminate opium production within 10 years.
The UN reports opium production has continued to grow in Afghanistan - by far the world's biggest poppy producer - despite several positive anti-drug steps by authorities recently.
"If we don't start translating counter-narcotics commitment into lower levels of production, we run the risk of (an) opium economy undermining all that has been achieved in creating a democratic new Afghanistan"
Antonio Maria Costa,
UNODC Executive Director
A survey released by the UNODC in October showed Afghanistan's estimated opium production rose 6% last year from 3400 tons to 3600 tons.
Opium is now cultivated in 28 of the country's 32 provinces, up from 18 provinces in 1999.
Already about 1.7 million Afghans, or 7% of the population, are thought to be involved in the industry.
Costa's remarks come after the recent publication of a Human Rights Watch report on Afghanistan, which documented how opium production had exploded in the country.
The rights organisation said in the absence of the Taliban, which in some years managed to stop nearly all poppy production, the industry is generating billions of dollars for forces outside the control of any legitimate authority.
"Much of this trade and the money it generates is under the control, or at least the influence, of various major and minor military commanders, who use this money to increase their military capability and gain independence from the central government and any international troops working with them," wrote report author Sam Zia-Zarifi.
However, HRW said these problems could have been avoided had the US and the international community acted more responsibly.
"Farmers who have waited futilely for agricultural assistance from the central government or the international community have turned to poppy cultivation," said the report.
"As a result, Afghanistan has regained its position as the world’s leading producer of heroin."